Gree is an investment company. It was never the plan to create something. Investments are usually a risk but you can keep it within limits. Spend a little and take a lot as long as possible ... how should that work for DS?
The result .. a lot of day 1 content that urgently needed an upgrade to keep players motivated and spend money.
It was still fun and it is a pity the gree did not have the courage to really develop the game.
If you as a company never have to ask the question of how to do things better. It is almost unbelievable that the game has lasted so long.